(a) Field of the Invention
The present invention concerns processes for the cryogenic separation of mixtures containing oxygen to give a product with a high concentration of oxygen, comprising the step of carrying out an exchange of heat and material in counter-current between a descending liquid and a rising gas in at least one transfer zone including a bundle of organized linings consisting of cross-undulated metallic layers.
(b) Description of Prior Art
A process and organized linings of this type have been described in the document WO-A-89/10527, in the name of the Applicant, of which the content is understood to be incorporated herein by reference.
In the known processes of this type, such as for the distillation of air, the metallic layers of lining are made from sheets having a thickness of 0.2 mm and have a specific surface of about 500 m.sup.2 /m.sup.3, the metal being stainless steel, aluminum or copper (see introduction of the presentation at the 1990 AIChE Loss Prevention Symposium of August 1990 in San Diego by Messrs. Dunbobbin, Werley and Hansel).
In practice, because of its cost and its performances, aluminum is the best material for most applications involving cryogenic separations. However, in the zones of high oxygen purity (higher than 98%), for example under elevated pressure, aluminum may present risks of ignition in linings of this type. This is the reason why it has been proposed (see the above mentioned presentation) to rely only on copper linings, in spite of the substantial cost increase thereof.